1. Field of the Invention
The present invention relates generally to power amplification.
2. Background Art
Class AB amplifiers are used in power-sensitive applications where the processed analog signals are characterized by a large crest factor (i.e., large ratio of peak value to root-mean-square (rms) value).
As opposed to class A amplifiers, class AB amplifiers have biasing currents that are signal-dependent. As such, when required by a large signal peak, they can source or sink tens of times more current than their quiescent bias currents.
One group of class AB amplifiers are the two-stage, Miller-compensated designs with a feedforward-biased class AB output stage and a class A input stage. These amplifiers have desirable characteristics, including large low-frequency gain, small output impedance, and a unity-gain bandwidth, which is not signal-dependent since the input stage transconductance is produced by a class A current.
However, with an output stage optimized for low power, the power dissipated by the class A input stage becomes important. There is a need therefore to reduce the power dissipated by the input stage.